1. Field of the Invention
The present invention relates generally to an NiCuZn-base ferrite and an electronic part using it, and more particularly to a ferrite used as a material for electronic parts that form a closed magnetic circuit and an electronic part fabricated using it.
2. Explanation of the Prior Art
So far, ferrites in the form of oxide magnetic materials containing Ni, Cu, Zn, etc., because of possessing good magnetic properties, have been used as core (magnetic core) materials for various electronic parts or as materials for inductor parts such as multilayer chip inductors.
For such magnetic cores or inductor parts, it is desired that, in consideration of varying temperature environments where they are used, the rate of changes in their initial permeability μi with changing temperatures be reduced or limited; that is, the temperature dependency of their initial permeability μi be in good condition (or fluctuate little with temperature).
Here, when it comes to an electronic part including a coil conductor such as a multilayer chip inductor, inductance can decrease depending on a current value as direct currents pass through the coil conductor in a closed magnetic circuit. For an electronic part, inductance decreases must be reduced as much as possible even with relatively large currents passing through it. It is thus desired that the rate of inductance changes be reduced or limited applying direct-current bias; that is, DC bias characteristics be in good condition.
To meet such demands, JP-A-2003-272912 has come up with an oxide magnetic material comprising an Ni—Cu—Zn ferrite material having a given composition as a main component with 0.2 to 3 wt % of SnO2 added to it for the purpose of achieving an oxide magnetic material that is used for an closed magnetic circuit-forming electronic part, and that, even at a large applied external stress, can ensure the desired magnetic properties and has good direct-current bias characteristics as well, and a multilayer electronic part using the same. The publication alleges that even at an applied compression stress of 40 MPa, the rate of change in its initial permeability is kept within 10%, and good direct-current bias characteristics is gained. By the addition of SnO2 alone, however, there would be no significant improvement in direct-current bias characteristics.
JP-A-2002-255637 has proposed an oxide magnetic porcelain composition comprising an Ni—Cu—Zn ferrite material having a given composition as a main component and further containing 1.5 percent by weight to 3.0 percent by weight of SnO2, 0.02 percent by weight to 0.20 percent by weight of Co3O4 and up to 0.45 percent by weight of Bi2O3 with a view to achieving an oxide magnetic porcelain composition with little or no characteristic value change due to temperature changes and, at the same time, with high specific resistance, and an inductor part using the same. The publication alleges that there is a high-performance electronic part obtainable, which has little or no characteristic value change due to temperature changes and, at the same time, has so high specific resistance that eddy-current losses are reduced with a Q value improvement.
However, the art of that publication is not to improve on direct-current bias characteristics, nor is there any disclosure of the composition of the invention in its specific examples. For instance, at the same initial permeability μi on the order of 80 to 130 with all other conditions being equal, there would be no NiCuZn-base ferrites as yet, where much improved direct-current bias characteristics as achieved herein is available.
Such being the situation, the invention has for its object the provision of a ferrite with a dramatic improvement in direct-current bias characteristics, and an electronic part using the same.